1. FIELD OF THE INVENTION
This invention relates generally to the use of a beam splitter for tracking and stabilizing light targets, and more particularly to a three-sided tracking sensor that employs three light detector elements.
2. DESCRIPTION OF THE RELATED ART
Various systems for the detection of the departure of a tracked point light target from an axis passing through the center of the tracking system are known. However, the known devices make use of a four-sided light splitter or of a four element detector for target tracking. For example, U.S. Pat. No. 4,234,145, which issued Nov. 18, 1980, to T. Leiboff, utilizes a lens and four photodetectors arranged in a square array. That system lacks tracking precision due to the physical gap necessary to separate the individual photodetectors.
In U.S. Pat. No. 4,225,781, which issued Sept. 30, 1980, to B. Hammons, a pyramidal tracking device is provided to shade photodetectors on each side of the pyramid when the base of the pyramid, which is the top of the tracking device, is facing the sun. However, this system being specifically designed as a sun tracker, blocks most of the light and cannot be used for tracking faint point light targets. U.S. Pat. No. 3,478,219, which issued Nov. 11, 1969, to G. Nutz, is intended as a sun tracker and utilizes a pyramidal prism to reflect the light laterally to respective photodetectors. U.S.S.R. Inventor's Certificate No. 678,465 utilizes a four-sided pyramid to refractively split a light beam into four components that are used for tracking. The tracking precision of that sensor is limited by the precision of the apex formed by the intersection of the four inclined sides of the pyramid.
Because the minimum number of components to determine the two-dimensional deviation of a tracked point light source is three, and because each of the above-identified tracking sensors has four components, one of the components is redundant.
It is an object of the present invention to provide a highly reliable and inexpensive tracking system.
It is another object of the present invention to provide a tracking sensor for use with extremely weak light sources having image diameters on the order of microns.
It is a further object of the present invention to provide a sensor having increased sensitivity by reducing the number of required light components to three.
It is a still further object of the present invention to increase the tracking precision of a tracking sensor by utilizing a sub-micron apex naturally formed by three intersecting inclined planes.